TRAMP is for transparently accessing remote files from within
Emacs. TRAMP enables an easy, convenient, and consistent
interface to remote files as if they are local files. TRAMP’s
transparency extends to editing, version control, and
TRAMP can access remote hosts using any number of access
methods, such as
related programs. If these programs can successfully pass
ASCII characters, TRAMP can use them. TRAMP
does not require or mandate 8-bit clean connections.
TRAMP’s most common access method is through
more secure alternative to
ftp and other older access
TRAMP on MS Windows operating systems is integrated with the
PuTTY package, and uses the
TRAMP mostly operates transparently in the background using the connection programs. As long as these programs enable remote login and can use the terminal, TRAMP can adapt them for seamless and transparent access.
TRAMP temporarily transfers a remote file’s contents to the local host editing and related operations. TRAMP can also transfer files between hosts using standard Emacs interfaces, a benefit of direct integration of TRAMP in Emacs.
TRAMP can transfer files using any number of available host
programs for remote files, such as
rsync or (under MS Windows)
provides easy ways to specify these programs and customize them to
specific files, hosts, or access methods.
For faster small-size file transfers, TRAMP supports encoded
transfers directly through the shell using
uuencode provided such tools are available on the remote
Accessing a remote file through TRAMP entails a series of actions, many of which are transparent to the user. Yet some actions may require user response (such as entering passwords or completing file names). One typical scenario, opening a file on a remote host, is presented here to illustrate the steps involved:
C-x C-f to initiate find-file, enter part of the TRAMP file name, then hit TAB for completion. If this is the first time connecting to that host, here’s what happens:
telnet, for example) in the buffer. If on the other hand, the login name was included in the file name portion, TRAMP sends the login name followed by a newline.
telnet). TRAMP displays the password prompt in the minibuffer. TRAMP then sends whatever is entered to the remote host, followed by a newline.
If TRAMP does not receive any messages within a timeout period (a minute, for example), then TRAMP responds with an error message about not finding the remote shell prompt. If there are any messages from the remote host, TRAMP displays them in the buffer.
For any ‘login failed’ message from the remote host, TRAMP aborts the login attempt, and repeats the login steps.
Note that for the remote shell, TRAMP invokes
/bin/sh. The remote host must recognize ‘exec /bin/sh’
and execute the appropriate shell. This shell must support Bourne
lscommands to find which files exist on the remote host. TRAMP sometimes uses
echowith globbing. TRAMP checks if a file or directory is writable with
test. After each command, TRAMP parses the output from the remote host for completing the next operation.
For inline transfers, TRAMP sends a command, such as ‘mimencode -b /path/to/remote/file’, waits until the output has accumulated in the buffer, then decodes that output to produce the file’s contents.
For external transfers, TRAMP sends a command as follows:
$ rcp user@host:/path/to/remote/file /tmp/tramp.4711
TRAMP reads the local temporary file /tmp/tramp.4711 into a buffer, and then deletes the temporary file.
I hope this has provided you with a basic overview of what happens behind the scenes when you open a file with TRAMP.